Hydraulic circuit for oil supply of an automatic, particularly a stepped automatic transmission for motor vehicles

ABSTRACT

The invention concerns a hydraulic circuit ( 3 ) for oil supply of an automatic transmission, in particular a stepped automatic transmission for motor vehicles, consisting of a low pressure circuit ( 4 ) for delivering a first volume stream V 1  at a first pressure level P 1  and a high pressure circuit ( 5 ) for delivering a second volume stream V 2  at a second, higher pressure P 2.    
     It is proposed that when necessary the first pressure level P 1  of the first volume stream V 1  can be modulated to the higher pressure P 2  and the two volume streams V 1,  V 2  can be summed at the same pressure level P 2.

The invention concerns a hydraulic circuit for oil supply of an automatic transmission, in particular a stepped automatic transmission for motor vehicles, according to the object of the Applicant's patent application with official file number 103 101 83.7.

In the practice, oil is supplied to automatic transmissions, in particular stepped automatic transmissions, by an oil pump formed as an internal gear-type pump, which is arranged in the area between the torque converter and the transmission housing and is driven on the engine side, i.e., via the pump impeller of the converter. With such a design, there is usually an under-supply at low engine speeds and an over-supply at high engine speeds, so the oil pump has to be controlled. This can be done—as proposed in WO 93/11376 by the present Applicant—by providing throttling means in the intake area, in which case, besides an internal gear-type pump, a radial piston pump is also found advantageous. Thanks to the intake-throttled pump, an almost constant delivery stream is obtained with an also nearly constant power increase from a certain drive speed.

A further improvement is given by so-termed tandem pumps, i.e., mechanically driven dual pump systems in which one of the two pumps is switched to unpressurized delivery at higher speeds. A further development of such a tandem pump was disclosed in WO 99/25979 by the Applicant, namely the combination of a conventional mechanical drive section with an electrical drive section for an oil pump, such that the electrical drive covers the lower speed range and the mechanical drive the upper speed range. This results in improved supply of the transmission.

A further proposal for adapting the oil delivery stream to the needs of the transmission was disclosed in DE-A 101 59 147 by the Applicant, in which an internal gear hydraulic pump has at least two pump stages, which deliver oil flows in their own pressure channels at different pressure levels. During this, the two pump stages can be switched on or off, depending on the situation, for example when a shift operation takes place, by virtue of a switching command and an increased oil demand for clutch filling has to be provided.

Further, DE-A 39 13 414 describes multi-circuit control pumps for supplying pressure medium to several hydraulic circuits with different and varying pressure and quantity requirements, in particular for the pressure, lubricant and coolant supply of CVT drive conceptions and automatic transmission controls. For this, a vane-type cell pump produces two or more delivery streams at different pressure levels and passes them respectively to the individual consumers. The individual consumers are thus each supplied by a single pump with delivery streams specifically adapted to their respective needs.

Another multi-circuit pump is disclosed in U.S. Pat. No. 5,722,815, such that an adjustable gerotor pump with three outlet ports on the pressure side produces three delivery streams, which can be turned on or off depending on the pump rotation speed so that in the upper speed ranges the pump power is adjusted downwards and power is saved.

Finally, in the older application by the present Applicant with file number 103 101 83.7, a multi-circuit radial piston pump is described, which delivers at least two part-streams at different pressure levels, which can be switched on or off as necessary.

The purpose of the present invention is to enable switching in a hydraulic circuit divided into a high pressure and a low pressure circuit for oil supply of an automatic transmission, in such a manner that the oil supply is adapted to the needs of the transmission.

This objective is achieved by the characteristics of Claim 1. It is provided that the two volume flows can, if necessary, be combined, according to the invention, so that a volume flow at high pressure can be delivered. For this, appropriate switching means are provided. The delivery streams, whether equal or different, are produced by any desired type of delivery elements known in their own right, such as gear-type pumps, vane cell pumps or radial piston pumps. Pumping can be carried out by a common pump with two delivery circuits or by two different pumps. According to the invention, the system allows the oil supply to be adapted to the current needs of the transmission and thus offers the advantage of power saving. There is a high or maximum oil demand on the high pressure side, in particular during a gearshift, when the shift elements have to be filled with pressure oil. Since gearshifts account statistically for a time fraction of only a few percent, at times other than during gearshifts, a smaller high pressure, volume flow, which suffices to compensate the leakage of the clutches, can be provided; in contrast, the second volume flow for lubrication and cooling can be provided at a lower pressure level. The resultant saving of drive power is also reflected by lower fuel consumption of the vehicle.

Advantageous features of the invention emerge from the subordinate claims. In a first variant according to the invention, the pressure in the high pressure circuit is adjusted by a pressure-relief valve and the pressure in the low pressure circuit by a pressure-relief valve that can be controlled by a pressure regulator. While the pressure-relief valve for the high pressure circuit is set for a constant pressure, the pressure-relief valve for the low pressure circuit can be varied, for example, being set to a high pressure during a gearshift. A delivery stream at the higher pressure level P2 is then also produced in the low pressure circuit. Advantageously, for this a one-way valve is provided between the two circuits, which opens into the high pressure circuit so that the two circuits are joined and a larger delivery stream is provided at the higher pressure level P2. After the gearshift, the setting of the pressure-relief valve in the low pressure circuit is restored to the pressure level P1 and the one-way valve closes.

In a second variant, a variable-path valve is provided for combining the two volume streams which, in a first switching position, allows the two volume streams to flow separately in parallel and in a second switching position combines them into a single stream, i.e., sums them. During this, the pressure-relief valve off the low pressure circuit is not functional, i.e., both delivery elements or pumps work against the pressure-relief valve with the higher pressure level P2.

In further advantageous embodiments of the invention, various pump concepts are provided such that, in a first design, the first delivery element for the low pressure circuit is driven electrically and the second delivery element for the high pressure is driven mechanically, in particular by the pump impeller of the torque converter of the stepped automatic transmission. It is possible, however, for both delivery elements for the high and low pressure to be integrated in one pump, i.e., a dual-circuit pump. As is known, the pumps can be internal or external gear-type pumps, radial piston pumps or vane cell pumps.

An example embodiment of the invention is represented in the drawing and will be described in more detail below. The figures show:

FIG. 1 is a schematic representation of a dual vane cell pump with asymmetrical volume flow division;

FIG. 2 is a first switching variant for summing the two volume flows; and

FIG. 3 is a second variant for summing the volume flows.

FIG. 1 shows a schematic representation of a dual vane cell pump 1, which delivers two volume streams V1 for a low pressure circuit (not shown) and a second volume stream V2 for a high pressure circuit (not shown). In the example embodiment illustrated, the delivery quantities of the volume streams V1 and V2 are different, as indicated by the different widths of the arrows V1, V2. The vane cell pump 1 has a rotor 2 with a mid-point M, which can be displaced to the left or the right in the Figures so that equal or different delivery quantities are obtained.

As already mentioned, the oil supply has to cover the needs both of lubrication and cooling and of filling the shift elements, namely clutches and brakes of the stepped automatic transmission, and this takes place at different pressure levels with equal or unequal delivery flows—which is why the total supply is divided into two volume streams V1, V2 at a low pressure level P1 and a high pressure level P2. The dual vane cell pump 1 is one example of many possible pump concepts for oil supply to a stepped automatic transmission for motor vehicles. The division into two volume streams could likewise be effected by a dual-circuit radial piston pump as in the older application with file number 103 101 83.7.

FIG. 2 shows a circuit diagram of a hydraulic circuit 3 (only partly represented) with a low pressure circuit 4 and a high pressure circuit 5, each supplied with hydraulic oil by a delivery element 6, 7, respectively. The high pressure circuit 5 is at a pressure level P2, which is maintained steady by a pressure-relief valve 8. This pressure level P2 corresponds to the main, operating or system pressure required for filling the shift elements (not shown). The low pressure circuit 4 is at a pressure level P1, which can be set by an adjustable pressure-relief valve 9. The electromagnetic adjustment is carried out by a pressure regulator (not shown). Between the low pressure circuit 4 and high pressure circuits 5 are arranged a connection line 10 with a one-way valve 11 which opens towards the high pressure circuit 5.

The circuit diagram shown enables two modes of operation, namely a first mode with two volume streams at different pressures P1, P2 and a second mode with only one volume stream at the higher pressure level P2.

During operation with two volume streams—at times other than during a gearshift—the adjustable pressure-relief valve 9 is set to the low pressure level P1 and the pump 6 delivers a volume stream V1 at pressure P1, via a line section 4 a, into the hydraulic circuit 3, i.e., mainly for lubrication and cooling purposes. In contrast, the pump 7 delivers a volume stream V2 at the higher pressure P2, via a line section 5 a, to the hydraulic circuit 3, this smaller volume stream V2 being used according to FIG. 1 to maintain the pressure in the shift elements, i.e., to compensate for oil leakage in them.

The second operating mode is initiated when a gearshift in the stepped automatic transmission is to take place. In that case, a larger volume flow at the high pressure level P2 is required. The pressure-relief valve 9 is, therefore, regulated by the pressure regulator and set to the high pressure level P2. This increases the pressure in the low pressure circuit 4 up to the high pressure P2, so that the one-way valve 11 opens and forms a connection to the high pressure circuit 5. The two pumps 6, 7—at maximum power—now deliver two volume streams at pressure level P2, which unite beyond the one-way valve 10 and pass into the hydraulic circuit 3 via the line section 5 a. The shift element provided for the gearshift can now be filled with pressure oil and the gearshift carried out. After the gearshift, the pressure regulator reduces the pressure in the pressure-relief valve 9 from P2 back to P1 so that two volume streams at different pressures are once more being delivered. The pump 6 then operates again at reduced power.

A variant of the design, represented in FIG. 2 (not shown), is to omit the one-way valve 11, so that the opening to the high pressure circuit 5 takes place because the pressure-relief valve 8 is moved to its “open” position by the high pressure in the low pressure circuit.

FIG. 3 shows a further example embodiment of the invention for a partially represented hydraulic circuit 12 with a modified circuit diagram for summing the two volume streams V1, V2; the same index numbers being used for the same components. The pump 7 and the pressure-relief valve 8 for setting the high pressure level P2 are provided in the high pressure circuit 5. With the low pressure circuit 4 comprising the pump 6 is associated a pressure-relief valve 13 which is set to the fixed low pressure level P1 and, in contrast to the pressure-relief valve 9 in FIG. 2, is therefore not adjustable. The delivery lines of the low pressure circuit 4 and high pressure circuit 5 are connected with one another by a controllable variable-path valve 14 with two switching positions 14 a, 14 b. The Figure shows the first valve position 14 a in which the volume streams V1 of the low pressure circuit 4 and V2 of the high pressure circuit 5 are separated from one another. The two volume streams at different pressure levels flow via the line sections 4 a, 5 a into the hydraulic circuit 12, analogously to the example embodiment of FIG. 2. In the second position of the variable-path valve 14, shown by the symbol 14 b, the two volume streams V1 from the low pressure circuit 4 and V2 from the high pressure circuit 5 are united. Thus the pump 6 works against the pressure-relief valve 8 with the high pressure level P2, so that a summed delivery stream at the high pressure level P2 is obtained which is passed via the line section 5 a into the hydraulic circuit 12. Analogously to the example embodiment of FIG. 2, in this valve position 14 b the gearshift can take place. After the shift, the variable-path valve 14 is restored to its position 14 a; the two circuits 4, 5 are then separated again, and the pump 6 again works against the pressure-relief valve 13 at the lower pressure level P1.

REFERENCE NUMERALS

1 dual vane cell pump

2 rotor

3 hydraulic circuit

4 low pressure circuit

4 a line section

5 high pressure circuit

5 a line section

6 first deliver element

7 second delivery element

8 pressure-relief valve (HP), fixed

9 pressure-relief valve (LP), adjustable

10 connection line

11 one-way valve

12 hydraulic circuit

13 pressure-relief valve (LP), fixed

14 variable-path valve

14 a first position

14 b second position

V1 first volume stream

V2 second volume stream

P1 low pressure

P2 high pressure

M mid-point of rotor 

1. Hydraulic circuit (3, 12) for oil supply of an automatic transmission, in particular a stepped automatic transmission for motor vehicles, consisting of a low-pressure circuit (4) for delivering a first volume stream V1 at a first pressure level P1 and a high pressure circuit (5) for delivering a second volume stream V2 at a second higher pressure P2, such that the first pressure level P1 of the first volume stream V1 can, when necessary, be modulated to the higher pressure level P2 and the two volume streams V1 and V2 can be summed at the same pressure level P2.
 2. Hydraulic circuit according to claim 1, characterized in that the summing of the volume streams V1, V2 takes place when a gearshift is initiated in the stepped automatic transmission.
 3. Hydraulic circuit according to claims 1 or 2, characterized in that a pressure-relief valve (8) is associated with the high pressure circuit (5) to maintain the pressure level P2.
 4. Hydraulic circuit according to claims 1, 2 or 3, characterized in that a pressure-relief valve (9) is associated with the low pressure circuit (4) to maintain the pressure level P1.
 5. Hydraulic circuit according to claim 4, characterized in that the pressure-relief valve (9) can be adjusted by a pressure regulator to change the pressure level P1, in particular to increase it to the pressure level P2.
 6. Hydraulic circuit according to any of claims 1 to 5, characterized in that a first delivery element (6) is associated with the low pressure circuit (4) to deliver the first volume stream V1 and a second delivery element (7) is associated with the high pressure circuit to deliver the second volume stream V2.
 7. Hydraulic circuit (3) according to any of claims 1 to 6, characterized in that a one-way valve (11) opening towards the high pressure circuit (5) is arranged between the high pressure circuit (5) and the low pressure circuit (4).
 8. Hydraulic circuit (12) according to any of claims 1 to 6, characterized in that the two volume streams V1, V2 can be summed by means of a switching variable-path valve (14).
 9. Hydraulic circuit (12) according to claim 8, characterized in that the variable-path valve (14) has two positions (14 a, 14 b), namely a first position (14 a) in which the two volume streams V1, V2 are separated and a second position (14 b) in which the two volume streams V1, V2 are combined.
 10. Hydraulic circuit according to claim 6, characterized in that the two delivery elements (6, 7) form a tandem pump.
 11. Hydraulic circuit according to claim 6, characterized in that the first delivery element (6) is formed as an electrically driven pump and the second delivery element (7) is formed as a mechanically driven pump, in particular driven by the pump impeller of the stepped automatic transmission.
 12. Hydraulic circuit according to claim 6, characterized in that the two delivery elements (6, 7) are formed as a dual-circuit pump.
 13. Hydraulic circuit according to claims 6, 10 or 12, characterized in that the delivery elements (6, 7) are formed as gear-type, radial piston or vane cell pumps. 